DESCRIPTION (verbatim from applicant's abstract): Prostate-specific antigen (PSA) is a kallikrein-like serine protease, expressed at very high levels by normal human prostate epithilium, epithelial cells in benign hyperplastic nodules and the majority of prostatic tumor cells in most prostate cancer. PSA and its complex with the serine proteinase inhibitor a1-antichymotrypsin have been widely used as markers for the diagnosis of prostate cancer. However, the molecular basis of regulatory role of PSA in the development of prostate cancer remains unclear. The long-term goal of this project is to understand the mechanism of PSA action, which will allow the development of more biologically effective substrates and inhibitors of PSA. This will improve the chemotherapy regimens and also give insights into the design of more specific reagents that can suppress the tumor growth in the prostate. This proposal describes experiments to probe the potential involvement of PSA proteolytic activity in primary and advanced prostate cancer and to elucidate the mechanism of action of PSA. The hypothesis for the mechanism will be tested through sequence-specific substrate and inhibitor design. The specific aims of this project are 1) to explore the nature of PSA hydrolysis of biological protein substrates by specifically examining natural substrates, such as IGFBP-3, fibronectin and collagenase in different stages of prostate cancer. 2) Synthetic peptide substrates will be developed for use as an effective assay to determine the stage of prostate cancer. The optimal synthetic peptide substrate of PSA will be generated by combinatorial library method. 3) The mechanistic similarity and structural specificity between PSA and other serine proteases such as chymotrypsin will be elucidated by fluorescence spectroscopy. The developed fluorogenic substrate in specific aim 2 will be used to study the kinetics of PSA reaction as well as other serine proteases. 4) The inhibition studies will be carried out by designing specific inhibitors through phosphonate ester derivatives. A series of peptidyl phosphonate esters will be synthesized followed by determining the potency of these compounds as inhibitors of the PSA.